1. Field of the Invention
The present invention relates to a cover-body locking construction for locking a covering state of a cover body provided to cover a structure detachably mounted into a specified housing, and an image forming apparatus provided with such a construction.
2. Description of the Related Art
An image forming apparatus as disclosed in Japanese Unexamined Patent Publication No. 2005-241840 is conventionally known. This image forming apparatus is used as a so-called copier for reading an image of a document by means of an image reader provided atop a box-shaped housing and transferring a toner image to a sheet based on the read image information. Such an image forming apparatus is provided in the housing with an image forming assembly including a photoconductive drum, a charger, an exposing device and a developing device, a fixing section including a fixing device comprised of a heating roller and a pressure roller whose outer circumferential surfaces are opposed to each other, and a sheet feeding section for storing sheets to be fed to the image forming section. A beam modulated based on the document image optically read by the image reader and emitted from the exposing device is device is projected onto the outer circumferential surface of the photoconductive drum rotating about its central axis and uniformly charged by the charger, thereby forming an electrostatic latent image on the outer circumferential surface of the photoconductive drum. The toner image is formed by supplying toner toward this electrostatic latent image from the developing device, and is transferred to a sheet fed from the sheet feeding section. The sheet after the transferring operation has the toner image fixed thereto by heating upon passing a nip between the heating roller and the pressure roller in the fixing device. The sheet after the image fixing operation is discharged onto a discharge tray provided on an outer wall of the housing.
In such an image forming apparatus, the respective devices such as the charger and the exposing device are formed into units together with accessories. These units are detachably mountable into the housing via specified frames. Various maintenance operations such as maintenance and inspection, exchange and jammed paper removal can be easily carried out by withdrawing the frames from the housing.
In the image forming apparatus of the above publication, the charger formed into a unit together with its accessories is also detachably mountable into the frame. Such a charger unit is fixed in the frame by a specified locking construction while being mounted at a position right above the photoconductive drum in the photoconductive drum in the frame. The locking construction is comprised of a hook portion provided at the other end of a fixed lever having one end thereof mounted on one lateral part of the frame in such a manner as to be rotatable about a shaft, and a locking portion provided at a position of the frame corresponding to the hook portion so as to be engageable with the hook portion. By pressing the fixed lever downward with the hook portion opposed to the locking portion, the hook portion is engaged with the locking portion after the fixed lever temporarily undergoes an elastic deformation to be deflected.
Accordingly, the fixed lever is elastically deformed to fit the hook portion into the locking portion to be engaged by strongly pressing the fixed lever downward after the charger unit is placed on the frame with the frame withdrawn from the housing and the fixed lever is turned about the shaft to press the charging unit. In this way, the charger unit is fixed to the frame. The charger unit is mounted into the housing by pushing the frame having the charger unit fixed thereto into the housing.
However, with this locking construction, there are cases where the hook portion of the fixed lever cannot be engaged with the locking portion of the frame due to an insufficient pressing force despite a downward pressing operation of the fixed lever to fix the charger unit to the frame withdrawn from the housing. Unless the hook portion is engaged with the locking portion, the engaged with the locking portion, the charger unit cannot be securely fixed by the fixed lever. If the frame should be pushed into the housing in such a state, the charger unit would be quite unstably mounted in the housing. Hence, the charger unit cannot properly give electric charges to the outer circumferential surface of the photoconductive drum during the later operation of the image forming apparatus, thereby causing such an inconvenience as to hinder the proper image forming operation.
Although an occurrence of such an inconvenience is described, taking the charger unit as an example with reference to the above patent publication, it is not limited to charger units. This holds for other devices such as developing devices and fixing devices provided that they are formed into units, detachably mountable into a frame, and a cover body is provided.